PARIS, Feb 28 (Reuters) - French utility EDF will not be allowed to start up its new Flamanville nuclear reactor without the approval by the country’s ASN regulator of a solution to sub-standard welding.

State-controlled EDF said last week that more than half of the weldings on the reactor’s secondary cooling circuit did not meet the required specifications.

It said this would not affect Flamanville’s safety or the schedule to load it with fuel at the end of 2018, however an ASN spokeswoman said on Wednesday the weldings problem could have an impact on the start-up calendar.

EDF’s Flamanville reactor - the same Areva-designed EPR reactor it is building in Hinkley Point, Britain - is years behind schedule and billions over budget.

The utility will have to present solutions to the ASN, which will then seek input from experts in the second half of this year, before deciding whether the weldings are fit for service, the spokeswoman said.

It seemed unlikely that ASN would receive a full report on the issue from EDF before the summer, she added.

In a statement on Wednesday, the ASN said that this report would have to measure the impact on reactor safety of the problems with the welding.

The reactor’s original safety documentation does not address the impact of a possible rupture of the weldings because they were designed to be rupture-proof.

The ASN said it had also asked EDF to study the possibility of repairing the weldings or replacing the piping.

In June, the ASN ruled that Flamanville’s vessel cover would have to be replaced just six years after startup because carbon concentrations in its steel could make it brittle. (Reporting by Geert De Clercq Editing by Jason Neely and Alexander Smith)